A detailed schematic description of the structural and functional organization of all the chromosomes in the genome of an organism.
A genome map may be defined as a detailed schematic description of the structural and functional organization of all the chromosomes in the genome of an organism. The most ambitious mapping project to date has been sequencing of the human genome, officially begun as the Human Genome Project.
DNA Sequencing: The ultimate goal in mapping a genome is to determine the complete nucleotide sequence of each chromosome. If a pure preparation of many copies of a DNA fragment up to about 800 base pairs in length is available, the sequence of the fragment can be determined by a sequencing machine. The study of DNA replication, in particular the isolation and investigation of DNA polymerase, has lead to the development of two technological advances in molecular biology: the chain termination method of DNA sequencing and the polymerase chain reaction (PCR).
The chain termination method (or dideoxy method) of DNA sequencing was first described by Fred Sanger in 1977, and in 1980 he was awarded the Nobel Prize for this work. This method of sequencing is based on a DNA synthesis reaction carried out in a test tube, using the DNA that is to be sequenced as a template. In addition to the normal deoxyribonucleotides (dATP, dCTP, dGTP and dTTP), DNA synthesis occurs in the presence of dideoxyribonucleotides(ddATP, ddCTP, ddGTP and ddTTP); they are capable of being added to newly synthesized DNA, but terminate any further extension of the strand because they lack the 3' hydroxyl necessary to form a phosphodiester bond with the next incoming nucleotide. Therefore, reactions are set up with denatured DNA template (the DNA fragment to be sequenced), a synthetic single – stranded DNA primer (analogous to the RNA primer during DNA replication), deoxyribonculeotides and DNA polymerase.
Illustration of DNA microarray.
It is a collection of microscopic DNA spots attached to a solid surface. DNA microarray that reveals expression levels of 2,400 human genes. DNA microarray analysis is one of the fastest – growing new technologies in the field of genetic research. Whole – Genome Shotgun Sequencing: It is also known as full genome sequencing, complete genome sequencing, or entire genome sequencing), is a laboratory process that determines the complete DNA sequence of an organism's genome at a single time. This entails sequencing all of an organism's chromosomal DNA as well as DNA contained in the mitochondria and, for plants, in the chloroplast. Almost any biological sample – even a very small amount of DNA or ancient DNA – can provide the genetic material necessary for full genome sequencing.